Project Summary Epilepsy is a disabling and costly disease that affects ~1% of the general population, requires long-term treatment and reduces productivity. For over 70% of patients, however, the underlying cause of epilepsy remains unknown, impeding effective diagnosis and treatment. Most forms of epilepsy have an underlying genetic basis; this ranges from single genes in Mendelian disorders, to multiple genes and environmental factors that collectively contribute to multifactorial complex epilepsy syndromes. Many genes involved in Mendelian epilepsy syndromes are known-the vast majority are autosomal dominant-however, autosomal dominant epilepsy genes do not significantly contribute to epilepsy in the general population. In contrast, the role of autosomal recessive epilepsy genes in complex epilepsy remains largely unexplored. There is a critical need to explore the role of identified autosomal recessive epilepsy syndrome genes in epileptogenic pathways, and to comprehensively characterize their pathophysiology in order to develop new therapeutic approaches. Our long-range goal is to define pathophysiologic mechanisms underlying human epilepsy and thereby improve the diagnosis and treatment of epilepsy. This proposal is built on our preliminary data and published reports demonstrating that 1) mutations in the PRICKLE genes cause epilepsy, 2) PRICKLE1 and the related PRICKLE2 protein play important roles in WNT-mediated signaling, which is implicated in critical biological processes such as neurodegeneration and neurodevelopment, and 3) the PRICKLE1 protein influences the normal function of REST, a critical repressor of neural genes. We hypothesize that mutations in PRICKLE genes can cause human epilepsy by perturbing PRICKLE function. The specific aims of this proposal are: 1) to screen a cohort of epilepsy patients for PRICKLE1 and PRICKLE2 variants to evaluate their role in complex epilepsy; 2) to define the functional effect of PRICKLE mutations on WNT-mediated signaling, REST-mediated transcriptional repression, and neurite extension in vitro; 3) to use zebrafish to define the functional effect of PRICKLE mutations in vivo, and; 4) to define the importance of PRICKLE mutations in vivo by assessing mice with mutations in the Prickle genes. The experimental design and methods to accomplish the first aim include direct sequencing and quantative PCR of the PRICKLE genes in a well-characterized cohort of patients with epilepsy and in a large control population. The second aim will involve cloning of mutant PRICKLE genes, gene silencing using PRICKLE-specific siRNA, and co-expressing PRICKLE binding partners by transient transfection to examine how PRICKLE mutations affect function. The third aim will use the zebrafish model to characterize human PRICKLE mutations. The fourth aim will use electroencephalography and histology to characterize electrophysiology and brain pathology in mice with Prickle mutations. Taken together, these assays will provide insights into how the PRICKLE gene functions are disrupted in human epilepsy.